LAMPEDUSA, Aug 20 (Reuters) - Nearly one hundred migrants who had been stranded on the Open Arms rescue ship off the coast of Lampedusa disembarked on the Italian island on Tuesday night, ending a prolonged stand-off between the Spanish charity operating the boat and the government in Rome.

The migrants, mainly from Africa, were removed from the boat after an Italian prosecutor ordered the seizure of the ship and the evacuation of the people on board.

The ship docked at Lampedusa's harbour just after 2330 CET (2230 GMT) on Tuesday.

The Open Arms ship, run by a Spanish charity of the same name, had rescued the migrants heading for Europe off the Libyan coast. But after Italy refused to let it dock the ship had been stranded at sea for nearly three weeks, with the charity saying that the migrants were distressed and urgently needed to find shelter.

Open Arms' director and founder, Oscar Camps, confirmed earlier on Twitter that the ship would be seized temporarily, adding it was "a cost that Open Arms assumes to ensure that people on board can be served."

"We consider it essential to prioritise the migrants' health and safety in this humanitarian emergency," he said.

Spain sent a naval vessel on Tuesday afternoon to rescue the migrants and take them to Mallorca after some of them jumped overboard.

But the Spanish navy is only due to reach Lampedusa in three days and Open Arms repeatedly said that the situation on board was desperate and some migrants were suicidal.

The passengers were sleeping jammed together on deck and sharing two toilets.

After the charity said nine had tried to swim ashore, Reuters footage showed another five people jump, although it was not immediately clear if some were lifeguards.

Italy has taken a tough line on migrant entry, saying it has borne too much responsibility for handling African migration to Europe. Interior Minister Matteo Salvini says the charity-run ships have become "taxis" for people smugglers.

"NO LONGER THE REFUGEE CAMP OF EUROPE"

Dozens of migrants have been taken ashore since the ship entered Italian waters because they were said to be minors or ill.

Salvini suggested on Tuesday that the charity was exaggerating the problems on board. Of eight migrants taken ashore on Monday night for urgent medical attention, he said, only two had health problems.

"Spanish NGO, Spanish ship, Spanish port: The coherence and strength of Italy has paid off. We are no longer the refugee camp of Europe," he said in a statement.

The standoff has fuelled Salvini's campaign against migrant boats from Africa, and comes as he is trying to force Italy into snap elections. Italy's Prime Minister Giuseppe Conte announced his resignation on Tuesday, accusing Salvini of sinking the ruling coalition for personal and political gain.

While welcoming Spain's latest move, Salvini's political rival Danilo Toninelli said he hoped Madrid would now commit to stop Open Arms' activity in the future.

Toninelli, who controls the Coast Guard but not port access, had earlier offered to take the migrants on a Coast Guard vessel to Spain under the condition that Madrid de-register the Open Arms ship by removing its Spanish flag.

"I hope that Spain answers our appeal and commits to stopping Open Arms in the future with the means and in the ways it deems right," the Italian minister said in a statement.

Without a flag, it would be difficult for the ship to continue running rescue missions.

Spain and five other European Union nations have offered to take the migrants. The details of the offers from Spain, France, Germany, Romania, Portugal and Luxembourg have yet to be finalised. (Reporting by Guglielmo Mangiapane and Wladimir Pantaleone; Additional reporting by Ashifa Kassam, Isla Binnie, Jose Elías Rodríguez, Belen Carreno, Elena Rodriguez and Ingrid Melander in Madrid, Stephen Jewkes in Milan, Crispian Balmer in Rome, Writing by Mark Bendeich and Pamela Barbaglia, Editing by Lisa Shumaker and Rosalba O'Brien)